Synthesis and complexation properties of a new tetraazatricarboxylate ligand

Abstract

A non-cyclic tetraazatricarboxylate ligand, tris(4-carboxy-3-methyl-3-azabutyl)amine (H₃L), derived from tris(2-aminoethyl)amine, was synthesised and purified. Its macroscopic and microscopic protonation behaviour was studied using potentiometry and proton NMR titrations, respectively. Stability constants for its complexes with Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Gd³⁺ were obtained potentiometrically and compared with those of related ligands. The structure, protonation and dynamics of the complexes of H₃L with Zn²⁺ and La³⁺ were investigated by proton NMR spectroscopy as a function of pH and the results were in accord with the potentiometric data for the complexes of Zn²⁺ and Gd³⁺. A nuclear magnetic relaxation dispersion study compared the water-proton relaxation parameters of [GdL] and [Gd(dtpa)]^2–(H₅dtpa =N,N,N′,N″,N″-diethylenetriaminepentaacetic acid), concluding that their water co-ordination numbers are the same but the former complex has a shorter electron-spin relaxation time.